Process for producing formaldehyde-treated starch free of unreacted or free formaldehyde

ABSTRACT

The invention is directed to a process for producing a formaldehyde-treated starch. A material which provides ammonium or amine groups is provided in a slurry of formaldehyde-treated starch containing free or unreacted formaldehyde at a pH of above about 6.5. The material combines with the free or unreacted formaldehyde and thus reduces vaporization of the formaldehyde.

United States Patent 91 Speakman [54] PROCESS FOR PRODUCINGFORMALDEHYDE-TREATED STARCH FREE OF UNREACTED OR FREE FORMALDEHYDE [75]Inventor: Edwin L. Speakman, Clinton, Iowa [73] Assignee: StandardBrands Incorporated, New

York, NY.

[22] Filed: Oct. 22, 1971 [21] Appl. No.: 191,816

[52] US. Cl. ...260/233.3 A, 260/2333 R, 260/2335 [51] Int. Cl. ..C08b19/01 [58] Field of Search ..260/233.3 A, 233.5, 233.3 R

[56] References Cited UNITED STATES PATENTS 3,549,618 12/1970 Speakman..260/233.3

[ Feb. 13, 1973 Primary Examiner-Donald E. Czaja AssistantExaminer-Melvyn I. Marquis Attorney-Aaron B. Karas et al.

[5 7] ABSTRACT 9 Claims, No Drawings THE INVENTION This inventionrelates to an improved process for producing a formaldehyde-treatedstarch.

it is known in the art that the properties of starch may be altered bytreating the same with formaldehyde. it is generally assumed thatformaldehyde reacts with starch under acidic conditions to cross-linkthe starch granules.

The prior art methods of treating starch with formaldehyde may begenerally classified into two broad classes. The first, and perhaps theone of principal importance to the starch industry, is treating starchwith formaldehyde under conditions such that the treated starch requiresslightly more rigorous conditions for pasting than does the starch priorto the fonnaldehyde treatment. The uses of such treated starches varywidely. For instance, the treated starches may be used for sizing ofpaper, textiles and as adhesives. Typical processes for producing suchformaldehyde-treated starches are disclosed, for example, in u. S. Pat.No. 3,360,5l2, to Moore and U. S. Pat. No. 2,113,034, to Rowland et al.

The other broad class of treating starch with formaldehyde includespreparing a formaldehyde-treated starch under such conditions as toobtain a starch product which is highly cross-linked. These crosslinkedstarch products tend not to disperse in water and maintain theirgranular characteristics even at high temperatures in the presence ofrelatively high concentrations of moisture. A typical process forpreparing these products is disclosed in U. S. Pat. No. 2,417,6l l, toPierson. A specific use for such starch products is as a dusting powder,for instance as surgical dusting powder.

Although processes for preparing formaldehydetreated starches varydepending upon the properties desired in the starch product, generallyformaldehyde and starch are reacted in an aqueous slurry in the presenceof a mineral acid catalyst. Usually, it is convenient to employformaldehyde in the form of the polymer, for instance, paraformaldehyde,since it is a solid material and convenient to handle. in such aprocess, a water slurry containing the starch and paraformaldehyde isprepared, and an acid is added to adjust the pH to cause reactionbetween the starch and formaldehyde.

The amount of formaldehyde required is dependent upon a number ofvariables, such as the pH of the slurry, the length of time that thereaction is allowed to proceed, the temperature at which the reaction iscarried out, the starch concentration of the slurry, and, of course, theproperties desired in the product. When a granular starch product isdesired, the reaction must be carried out below temperatures which willgelatinize the starch. Temperatures in the range of from about 118 toabout 130 F are suitable for this purpose. Higher temperatures may beemployed when gelatinization inhibitors are present, such as NaCl andthe like.

Preferably, the reaction is carried out in a starch slurry having aconcentration of from about 16 to about 22 Baume (28 per cent to 39 percent starch on a dry solids basis). The pH during the reaction may be inthe range of from about L7 to about 2.5 and the paraformaldehydeconcentration may be in the range of from about 0.25 to about 5 percent, based on the dry substance starch. The reaction time depends uponthe viscosity characteristics desired, and may be in the range of fromabout 3 to 15 hours.

When the reaction has proceeded to the desired extent, sufficient alkaliis added to terminate the reaction. This occurs at a pH of above about3. The treated starch product'can be separated from the slurry byconventional means. These may include sieving the slurry to removenon-starch materials and filtering, for instance on a vacuum drumfilter. The starch product may then be dried at conventional starchdrying temperatures, for example at air temperatures of from about 160to 300 F. Depending upon the starch concentration of the slurry, it issometimes advisable to dilute the slurry prior to the sieving thereof soas to effect an increased flow rate through the sieve. Because of thetemperatures employed to effect reaction of the starch withformaldehyde, the starch slurry during this separation process may be atrelatively high temperatures, for instance above ambient temperature toabout F.

in commercial production of formaldehyde-treated starch, generally,there will be present after the reaction of formaldehyde and starch,unreacted or free formaldehyde. This formaldehyde is extremelyundesirable because of its tendency to volatilize at low temperatures.This presents potential health hazards to those who are present in thevicinity of the separation process and to those who are present duringthe use of such a starch product. Even at extremely low concentrations,volatilized formaldehyde is irritating.

U. S. Pat. No. 3,549,618, to Speakman discloses a method whereinsulfites, bisulfites and hydrosulfites are used to eliminate free orunreacted formaldehyde from formaldehyde-treated starch. Although thismethod has solved the problem commonly associated with preparingformaldehyde-treated starch, there are a number of problems associatedtherewith. These include economics and potential pollution problems. Forinstance, due to the salts formed by using the sulfites and because itis desirable to remove at least a major portion of the same from theformaldehyde derivatives of starch, these soluble salts increase theburden on sewage disposal facilities. in the method of the presentinvention not only is free or unreacted formaldehyde eliminated fromformaldehyde-treated starch, but a much lesser amount of reactionbyproducts are formed, thus decreasing the burden on sewage disposalfacilities.

The method of the present invention is accomplished by providing in anaqueous slurry of formaldehydetreated starch at a pH of above about 6.5containing unreacted or free formaldehyde a material which solubilizesto yield ammonium or amine groups which react at a pH of above about 6.5with the free or unreacted formaldehyde to substantially reducevaporization of the same.

The term starch includes all raw starches, e.g., corn, tapioca, wheat,waxy sorghum, waxy maize, grain sorghum, rice and the like, and variousmodified starches and derivatives of starches, e.g., thin-boilingstarches, oxidized starches, starch ethers, starch esters and the like,the only requirement being that the starch contain free hydroxyl groups.

The material which provides ammonium or amine groups may be incorporatedinto the aqueous slurry of formaldehyde-treated starch in any convenientmanner. When the formaldehyde-starch reaction has been completed, it ispreferred to incorporate this material into the slurry after the slurryhas been made alkaline. The pH of the slurry must be above about 6.5 forreaction to occur between the free formaldehyde and the ammonium oramine groups-The pH should not be so high as to damage or geiatinize thestarch granules. The typical pH range within which the reaction iseffected is from about 7 to below about 1 1.5 The preferred pH, however,is in the range of from about 7.5 to about 9.5. The preferred materialused in the present method is ammonium hydroxide.

Any base or substance which in water solution will decompose to yield abase may be used to adjust the pH of the formaldehyde reaction slurry toabove about 6.5. The preferred base is sodium carbonate because ofeconomics and ease of handling. lf the material used to provide ammoniumor amine groups is sufficiently basic, it may also be employed to raisethe pH of the reaction slurry to above about 6.5. Any combination ofbases may be used for the pH adjustment.

The amount of material used to provide ammonium or amine groups in theformaldehyde-starch reaction slurry is preferably sufficient to reactsubstantially stoichiometrically with the free or unreactedformaldehyde. if this material is also used to adjust the pH of thereaction slurry to above about 6.5 then more material must be providedto effect reaction with the free or unreacted formaldehyde.

After the free or unreacted formaldehyde is eliminated, it is generallynecessary to lower the pH of the slurry to a range of from about 3.5 toabout 8.0. The reason for lowering the pH of the slurry to within thisrange is that the user of the formaldehyde-treated starch generallyprefers starch products within this pH range and these pHs are normal tothe industry.

in order to more clearly describe the nature of the present invention,specific examples will hereinafter be described. it should beunderstood, however, that this is done solely by way of example, and isintended neither to delineate the scope of the invention nor limit theambit of the appended claims. in the example and throughout thisspecification, percentages are intended to refer to per cent by weight,unless otherwise specified.

EXAMPLE I A corn starch slurry containing 35.5 per cent dry basis starchriatic acid to a pH of 1.5 and 0.8 per cent paraformaldehyde added basedupon the starch solids present. The slurry was maintained under theseconditions for about 5 hours and then neutralized to a pH of about 7with a Na CO solution. 77.8 per cent ammonium hydroxide, based on theweight of the paraformaldehyde, was added to the slurry. The pH of theslurry was 8.8. The slurry was stirred for two hours and then the pH waslowered to 4.0 by the addition of muriatic acid. The slurry was filteredon a rotary vacuum filter was heated to [29 F, acidified with mu-' torecover the formaldehyde-treated starch. The starch cake was washed onthe filter and dried in a Proctor & Schwartz drier at an air temperatureof 200 F. No formaldehyde odor was detected during the separation,drying or evaluation of the product. Also, the viscosity characteristicsof the product were unaffected by the ammonium treatment.

EXAMPLE I! This Example illustrates the effect of pH of an aqueousslurry of formaldehyde on elimination of unreacted or free formaldehyde.

A corn starch slurry containing 39.09 per cent dry basis starch washeated to 129 F, acidified with muriatic acid to a pH of 1.5 and 0.8 percent paraformaldehyde added based upon the starch solids present. Theslurry was maintained, with stirring, under these conditions for 1 hourand then the pH of the slurry was adjusted to 4.0 bythe addition of a NaCO solution. Sufficient ammonium chloride was added to the slurry toprovide a concentration of 1.3] per cent based on the dry basis starchpresent. The slurry was divided into 6 portions and the pH of theportions adjusted by the addition of a Na, CO solution to the valuesshown in Table 1 below. The slurries were stirred for about 17 hours andthen the odor of the slurries was determined.

TABLE I Odor of Aqueous Slurries of Formaldehydc- Treated Starch atVarious pH Levels The pHs of the above slurries were adjusted to 5.6with a solution of sodium carbonate or muriatic acid, as required, andfiltered. The odor of the filter cakes was determined. The results areshown in Table I].

TABLE ll Odor of Filter Cakes of Formaldehyde-treated Starch Filter Cakeobs ervations Strong formaldehyde odor Strong formaldehyde odor Strongformaldehyde odor No formaldehyde odor No fonnaldehyde odor Noformaldehyde odor The wet filter cakes were then dried in a laboratorymodel Proctor & Schwartz drier at an air temperature of 180 F and theodor of the hot exhaust air determined. The results are shown in TableIll.

TABLE III Odor of Hot Exhaust Air From Drying Formaldehydetreated StarchFilter Cake Observations A Strong formaldehyde odor B Strongformaldehyde odor C Strong formaldehyde odor D Slight formaldehyde odorE No formaldehyde odor F No formaldehyde odor From the above, it isapparent that in order to reduce or eliminate the vaporization ofunreacted or free formaldehyde from formaldehyde-treated starch, the pHof above about 6.5 is necessary.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and it is not intended to exclude anyequivalents of the features shown or described or portions thereof,since it is recognized that various modifications are possible withinthe scope of the invention claimed.

What is claimed is:

l. A process for producing a formaldehyde-treated starch comprisingreacting starch and formaldehyde in an aqueous slurry under conditionswhereby unreacted or free formaldehyde is present in the slurry,adjusting the pH of the slurry from above about 6.5 to below a levelwhere gelatinization of the starch occurs and providing in the slurry asufficient amount of a material which solubilizes to yield ammonium oramine groups which react at a pH of above 6.5 with the unreacted or freeformaldehyde to substantially reduce the vaporization thereof. 7

2. A process for producing a formaldehyde-treated starch as defined inclaim 1, wherein the pH of the slurry is maintained in the range of fromabove about 7 to below about 11.5 during the reaction of the ammonium oramine groups with the unreacted or free frmal- 6 dehyde.

3. A process for producing a formaldehyde-treated starch as defined inclaim 2, wherein the pH of the slurry is maintained in the range of fromabout 7.5 to about 9.5 during the reaction of the ammonium or aminegroups with the unreacted or free formaldehyde.

4. A process for producing a formaldehyde-treated starch as defined inclaim 2, wherein the material provided in the aqueous slurry is ammoniumhydroxide.

5. A process for producing a formaldehyde-treated starch as defined inclaim 3, wherein the material provided in the aqueous slurry is ammoniumhydroxide.

6. A process for producing a formaldehyde-treated starch as defined inclaim 4, wherein after the ammonium groups have reacted with theformaldehyde the pH of the slurry is lowered to the range of from about3.5 to about 8.

7. A process for producing a formaldehyde-treated starch as defined inclaim 6, wherein the starch and formaldehyde are reacted at a pH withinthe range of from about 1.7 to about 2.5 and the pH of the slurry isadjusted to above about 7 by the addition of sodium carbonate.

8. A process for producing a formaldehyde-treated starch as defined inclaim 2, wherein the material provided in the aqueous slurry is anammonium salt.

9. A process for producing a formaldehyde-treated starch as defined inclaim 8, wherein the material provided in the aqueous slurry is ammoniumchloride.

1. A process for producing a formaldehyde-treated starch comprisingreacting starch and formaldehyde in an aqueous slurry under conditionswhereby unreacted or free formaldehyde is present in the slurry,adjusting the pH of the slurry from above about 6.5 to below a levelwhere gelatinization of the starch occurs and providing in the slurry asufficient amount of a material which solubilizes to yield ammonium oramine groups which react at a pH of above 6.5 with the unreacted or freeformaldehyde to substantially reduce the vaporization thereof.
 2. Aprocess for producing a formaldehyde-treated starch as defined in claim1, wherein the pH of the slurry is maintained in the range of from aboveabout 7 to below about 11.5 during the reaction of the ammonium or aminegroups with the unreacted or free formaldehyde.
 3. A process forproducing a formaldehyde-treated starch as defined in claim 2, whereinthe pH of the slurry is maintained in the range of from about 7.5 toabout 9.5 during the reaction of the ammonium or amine groups with theunreacted or free formaldehyde.
 4. A process for producing aformaldehyde-treated starch as defined in claim 2, wherein the materialprovided in the aqueous slurry is ammonium hydroxide.
 5. A process forproducing a formaldehyde-treated starch as defined in claim 3, whereinthe material provided in the aqueous slurry is ammonium hydroxide.
 6. Aprocess for producing a formaldehyde-treated starch as defined in claim4, wherein after the ammonium groups have reacted with the formaldehydethe pH of the slurry is lowered to the range of from about 3.5 to about8.
 7. A process for producing a formaldehyde-treated starch as definedin claim 6, wherein the starch and formaldehyde are reacted at a pHwithin the range of from about 1.7 to about 2.5 and the pH of the slurryis adjusted to above about 7 by the addition of sodium carbonate.
 8. Aprocess for producing a formaldehyde-treated starch as defined in claim2, wherein the material provided in the aqueous slurry is an ammoniumsalt.